Multi-fuel engine, and fuel injection method in a multi-fuel engine

Abstract

The objective is to provide a multi-fuel engine capable of further improving the combustibility of the main fuel, and a fuel injection method for a multi-fuel engine. [Solution] The multi-fuel engine of the present invention comprises a cylinder that defines a part of the combustion chamber, a first injection unit that injects ignition fuel into the combustion chamber, and a second injection unit that injects main fuel into the combustion chamber. The cylinder head of the cylinder has an intake valve and an exhaust valve, and the first injection unit and the second injection unit are arranged on the cylinder head. The second injection unit injects more of the main fuel into the exhaust valve side of the combustion chamber than into the intake valve side.

Description

Technical Field

[0001] The present invention relates to a multi-fuel engine capable of using a plurality of types of fuels, and a fuel injection method in the multi-fuel engine.

Background Art

[0002] Conventionally, a multi-fuel engine capable of corresponding to a plurality of types of fuels has been known (see Patent Document 1). Since the ignition property of fuels varies depending on the type, in order to correspond to a plurality of types of fuels, it is necessary to correspond to fuels with poor ignition properties. In a multi-fuel engine, when using a fuel with poor ignition properties as the main fuel, a fuel with better ignition properties than this fuel (ignition fuel) is ignited, and this is used as a kindling to burn the main fuel.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the multi-fuel engine as described above, in recent years, it has been required to further improve the combustibility of the main fuel.

[0005] Therefore, an object of the present invention is to provide a multi-fuel engine capable of further improving the combustibility of the main fuel, and a fuel injection method in the multi-fuel engine.

Means for Solving the Problems

[0006] The multi-fuel engine of the present invention includes: a cylinder defining a part of the combustion chamber; a first injection unit for injecting ignition fuel into the combustion chamber; a second injection unit for injecting main fuel into the combustion chamber, The cylinder head of the aforementioned cylinder has an intake valve and an exhaust valve. The cylinder head is equipped with the first injection unit and the second injection unit. The second injection unit injects more of the main fuel into the exhaust valve side of the combustion chamber than into the intake valve side.

[0007] During engine operation, the combustion chamber becomes hotter on the exhaust valve side than on the intake valve side. Therefore, as in the above configuration, more main fuel is injected into the exhaust valve side than the intake valve side in the combustion chamber, making the main fuel easier to burn due to the high temperature. In other words, the combustibility of the main fuel is improved.

[0008] In the aforementioned multi-fuel engine, The injection center of the second injection unit may be located closer to the exhaust valve than to the intake valve.

[0009] In this way, by shifting the injection center of the second injection unit towards the exhaust valve side in the combustion chamber, more of the main fuel is injected towards the exhaust valve side, which makes it easier for the main fuel to burn.

[0010] Furthermore, in the aforementioned multi-fuel engine, When viewed from the central axis direction of the cylinder, assuming a first imaginary line that passes through an intermediate position between the intake valve and the exhaust valve and divides the combustion chamber into a first region where the intake valve is located and a second region where the exhaust valve is located, and a second imaginary line perpendicular to the first imaginary line at the position of the central axis, The injection center of the second injection unit may be located on the second imaginary line at a position closer to the exhaust valve side than the central axis.

[0011] In this way, by shifting the injection center of the second injection unit toward the exhaust valve on the second imaginary line, more of the main fuel is injected toward the exhaust valve side in the combustion chamber, which makes it easier for the main fuel to burn.

[0012] Furthermore, in the aforementioned multi-fuel engine, When viewed from the central axis direction of the cylinder, assuming a first imaginary line that passes through an intermediate position between the intake valve and the exhaust valve and divides the combustion chamber into a first region where the intake valve is located and a second region where the exhaust valve is located, and a second imaginary line perpendicular to the first imaginary line at the position of the central axis, The injection center of the second injection unit may be located at a position closer to the exhaust valve side than the position of the central axis in the direction of the second virtual line, and at a position closer to one side than the position of the central axis in the direction of the first virtual line.

[0013] Thus, even if the injection center of the second injection unit is not located on the second dashed line, if it is shifted towards the exhaust valve, more of the main fuel will be injected towards the exhaust valve in the combustion chamber, which makes it easier for the main fuel to burn.

[0014] Furthermore, in the aforementioned multi-fuel engine, The second injection unit has an injection hole into which the main fuel is injected, When the combustion chamber is divided into a first region where the intake valve is located and a second region where the exhaust valve is located, the injection port may be configured to inject more of the main fuel into the second region than into the first region.

[0015] In this way, the configuration of the injection holes allows more of the main fuel to be injected into the second region, which makes the main fuel easier to burn.

[0016] Furthermore, in the aforementioned multi-fuel engine, The injection holes are arranged in a plurality at intervals in the circumferential direction centered on the injection center of the second injection unit. The diameter of the injection hole for injecting the main fuel into the second region may be larger than the diameter of the injection hole for injecting the main fuel into the first region.

[0017] In this way, by increasing the diameter of the injection holes that inject the main fuel into the second region, more of the main fuel can be injected into the second region, which makes the main fuel easier to burn.

[0018] Also, in the multi-fuel engine, The injection holes are arranged in a circumferential direction at intervals around the injection center of the second injection part, The number of the injection holes for injecting the main fuel into the second region may be larger than the number of the injection holes for injecting the main fuel into the first region.

[0019] In this way, by increasing the number of the injection holes for injecting the main fuel into the second region, more main fuel can be injected into the second region, and thereby, the main fuel becomes easier to burn.

[0020] Also, in the multi-fuel engine, The second injection part may be arranged such that the injection center of the main fuel is closer to the intake valve than the exhaust valve.

[0021] In this way, even if the injection center of the second injection part is located on the intake valve side, more main fuel is injected on the exhaust valve side in the combustion chamber, and thereby, the main fuel becomes easier to burn.

[0022] Also, the fuel injection method in the multi-fuel engine of the present invention is In a multi-fuel engine including a cylinder head provided with an intake valve and an exhaust valve and defining a part of a combustion chamber, and in which ignition fuel and main fuel are injected into the combustion chamber, More main fuel is injected into the combustion chamber from the intake valve side toward the exhaust valve side.

[0023] In the combustion chamber during engine operation, the exhaust valve side becomes hotter than the intake valve side. Therefore, by injecting more main fuel into the combustion chamber from the intake valve side toward the exhaust valve side as in the above configuration, the main fuel becomes easier to burn.

Advantages of the Invention

[0024] Based on the above, the present invention provides a multi-fuel engine that can further improve the combustibility of the main fuel, and a fuel injection method in a multi-fuel engine. [Brief explanation of the drawing]

[0025] [Figure 1] Figure 1 is a schematic diagram illustrating the configuration of a multi-fuel engine according to this embodiment. [Figure 2] Figure 2 is a diagram illustrating the configuration of the first injection unit and the second injection unit of the multi-fuel engine. [Figure 3] Figure 3 is a schematic diagram showing the state in which the first injection unit injects ignition fuel. [Figure 4] Figure 4 is a schematic diagram showing the state in which the second injection unit injects the main fuel. [Figure 5] Figure 5 is a schematic diagram showing the state in which the first and second injection units inject fuel. [Figure 6] Figure 6 is a schematic diagram showing the state in which the second injection unit of a multi-fuel engine according to another embodiment injects the main fuel. [Figure 7] Figure 7 is a schematic diagram showing the state in which the second injection unit of a multi-fuel engine according to another embodiment injects the main fuel. [Figure 8] Figure 8 is a schematic diagram showing the state in which the second injection unit of a multi-fuel engine according to another embodiment injects the main fuel. [Modes for carrying out the invention]

[0026] The following describes one embodiment of the present invention with reference to Figures 1 to 5.

[0027] The multi-fuel engine of this embodiment is an engine that can use multiple types of fuel, for example, methanol (main fuel) and heavy oil (ignition fuel). This multi-fuel engine is a diesel engine (that is, an engine that operates by igniting fuel sprayed into a combustion chamber that has been heated to a high temperature by compressing air), and it is an engine that does not use a spark plug. The multi-fuel engine of this embodiment is a so-called direct injection engine in which fuel is directly injected (sprayed) into the combustion chamber, and is installed, for example, on a ship.

[0028] As shown in Figure 1, the multi-fuel engine 1 of this embodiment comprises a cylinder 3 that defines a part of the combustion chamber 4, a first injection unit 5 that injects ignition fuel into the combustion chamber 4, and a second injection unit 6 that injects main fuel into the combustion chamber 4. This multi-fuel engine 1 injects more main fuel into the combustion chamber 4 on the exhaust valve 32 side than on the intake valve 31 side.

[0029] Specifically, the multi-fuel engine 1 comprises an engine body 2 having a cylinder 3 that defines a part of the combustion chamber 4, a first injection unit 5, a second injection unit 6, a first fuel pump P1 that supplies ignition fuel to the first injection unit 5, and a second fuel pump P2 that supplies main fuel to the second injection unit 6. The multi-fuel engine 1 also comprises main motion system components.

[0030] The engine body 2 includes a cylinder block 21, a cylinder head 22, and a crankcase 23, and the cylinder block 21 and the cylinder head 22 constitute a cylinder 3. The engine body 2 in this embodiment has a plurality of cylinders 3.

[0031] The cylinder 3, together with the piston 10 described later, constitutes (defines) the combustion chamber 4. This combustion chamber 4 is the space surrounded by the cylinder block 21, the cylinder head 22, and the piston 10, and in this embodiment, the combustion chamber 4 is a roughly cylindrical space.

[0032] The cylinder head 22 of cylinder 3 has an intake valve 31 and an exhaust valve 32. The intake valve 31 and exhaust valve 32 of cylinder 3 are opened and closed by a camshaft. Specifically, the camshaft rotates due to power (rotational power) transmitted from the crankshaft 11 (described later) via a belt, gears, etc., thereby opening and closing the intake valve 31 and exhaust valve 32.

[0033] When the cylinder head 22 is viewed from the direction of the central axis of the cylinder 3 (combustion chamber 4), as shown in Figure 3, the intake valve 31 is located in the region (first region) Ar1 on one side (right side in Figure 3) of the first imaginary line K1 passing through the central axis C of the cylinder 3, and the exhaust valve 32 is located in the region (second region) Ar2 on the other side (left side in Figure 3). In the following, the imaginary line that is perpendicular to the first imaginary line K1 at the position of the central axis C will be referred to as the second imaginary line K2.

[0034] In the cylinder head 22 of this embodiment, two intake valves 31 are located in the first region Ar1, and two exhaust valves 32 are located in the second region Ar2. The distance between the two intake valves 31 and the first virtual line K1 in the direction of the second virtual line K2 is the same as the distance between the two exhaust valves 32 and the first virtual line K1 in the direction of the second virtual line K2. That is, when viewing the cylinder 3 from the direction of the central axis C, the first virtual line K1 passes through an intermediate position between the intake valves 31 and the exhaust valves 32, dividing the combustion chamber 4 into the first region Ar1 where the intake valves 31 are located and the second region Ar2 where the exhaust valves 32 are located.

[0035] Furthermore, the two intake valves 31 are positioned in the direction of the first virtual line K1 with a gap between them, and the two exhaust valves 32 are also positioned in the direction of the first virtual line K1 with a gap between them. More specifically, the two intake valves 31 are positioned such that the second virtual line K2 is located midway in the direction of the first virtual line K1, and the two exhaust valves 32 are also positioned such that the second virtual line K2 is located midway in the direction of the first virtual line K1.

[0036] The first fuel pump P1 is connected to the first injection unit 5 by the first supply pipe 7A, and supplies ignition fuel to the first injection unit 5 through the first supply pipe 7A.

[0037] The second fuel pump P2 is connected to the second injection unit 6 by a second supply pipe 7B, and supplies the main fuel to the second injection unit 6 through the second supply pipe 7B. In this embodiment, the amount of main fuel supplied to the second injection unit 6 by the second fuel pump P2 is greater than the amount of ignition fuel supplied to the first injection unit 5 by the first fuel pump P1.

[0038] The first injection unit 5 is a so-called injector, and as shown in Figure 2, it has a first injection hole 51 at the tip of the nozzle that injects ignition fuel supplied by the first fuel pump P1 into the cylinder 3 (combustion chamber 4). The first injection unit 5 in this embodiment has a plurality of first injection holes 51, and these plurality of first injection holes 51 are spaced apart in the circumferential direction around the central axis (first injection center) C1 of the first injection unit 5. More specifically, each of the plurality of first injection holes 51 is a hole of the same diameter and is spaced equally apart in the circumferential direction. As a result, the first injection unit 5 can inject the ignition fuel F1 without bias in the circumferential direction around the first injection center C1 (see Figure 3).

[0039] As shown in Figure 3, the first injection unit 5 is positioned on the cylinder head 22 such that the first injection center C1 coincides with the central axis C of the cylinder 3. As a result, the first injection unit 5 injects the same amount or approximately the same amount of ignition fuel into the first region Ar1 and the second region Ar2.

[0040] The second injection unit 6 is a so-called injector, and as shown in Figure 2, it has a second injection hole 61 at the tip of the nozzle that injects the main fuel supplied by the second fuel pump P2 into the cylinder 3 (combustion chamber 4). The second injection unit 6 in this embodiment has a plurality of second injection holes 61, and these plurality of second injection holes 61 are spaced apart in the circumferential direction around the central axis (second injection center) C2 of the second injection unit 6. More specifically, the plurality of second injection holes 61 (the same number as the first injection holes 51) are holes of the same diameter and are spaced equally apart in the circumferential direction. As a result, the second injection unit 6 can inject the main fuel F2 without bias in the circumferential direction around the second injection center C2 (see Figure 4). In addition, each second injection hole 61 in this embodiment is positioned to inject the main fuel F2 at a position shifted in the circumferential direction relative to the ignition fuel F1 injected from the first injection hole 51 of the first injection unit 5 (i.e., a position shifted in phase in the circumferential direction relative to the first injection hole 51 of the first injection unit 5) (see Figure 5).

[0041] As shown in Figure 4, the second injection unit 6 is positioned on the cylinder head 22 such that the second injection center C2 is offset from the central axis C of the cylinder 3 toward the exhaust valve 32 on the second dashed line K2. As a result, the second injection unit 6 injects more main fuel into the second region Ar2 than into the first region Ar1.

[0042] Furthermore, the main moving system components include a piston 10, which is arranged within the cylinder 3 so as to be able to reciprocate and, as shown in Figure 1, constitutes the combustion chamber 4 together with the cylinder 3; a crankshaft 11, which converts the reciprocating motion of the piston 10 into rotational motion and outputs it; a connecting rod 12, which connects the piston 10 and the crankshaft 11; and a flywheel (not shown), which is arranged on the crankshaft 11 and suppresses rotational unevenness (torque fluctuations) of the multi-fuel engine 1 by inertial force.

[0043] The multi-fuel engine 1 described above comprises a cylinder 3 that defines a portion of the combustion chamber 4, a first injection unit 5 that injects ignition fuel into the combustion chamber 4, and a second injection unit 6 that injects main fuel into the combustion chamber 4. The cylinder head 22 of the cylinder 3 has an intake valve 31 and an exhaust valve 32, and the first injection unit 5 and the second injection unit 6 are arranged in the cylinder head 22, with the second injection unit 6 injecting more main fuel into the exhaust valve 32 side of the combustion chamber 4 than into the intake valve 31 side.

[0044] In the combustion chamber 4 of the multi-fuel engine 1, the exhaust valve 32 side becomes hotter than the intake valve 31 side. As a result, more of the main fuel is injected from the intake valve 31 side to the exhaust valve 32 side in the combustion chamber 4, and the high temperature makes the main fuel easier to burn. In other words, the combustibility of the main fuel is improved in the multi-fuel engine 1. Further details are as follows.

[0045] The main fuel (e.g., methanol) is a so-called flame-retardant fuel and is difficult to ignite by compression by the piston 10 alone in the cylinder 3 of the multi-fuel engine 1. Therefore, in the multi-fuel engine 1 of this embodiment, the main fuel sprayed into the cylinder 3 (i.e., the combustion chamber 4) ignites an ignition fuel (e.g., heavy oil) that is more ignitable than the main fuel, and burns using this as an ignition source.

[0046] In the combustion of the main fuel in the combustion chamber 4, the exhaust valve 32 side (second region Ar2) is usually hotter than the intake valve 31 side (first region Ar1). Therefore, in the multi-fuel engine 1 of this embodiment, the main fuel is injected into the exhaust valve 32 side in the combustion chamber 4, that is, more main fuel is injected into the higher temperature region, thereby further improving the combustibility of the main fuel.

[0047] Furthermore, in the multi-fuel engine 1 of this embodiment, the second injection center C2 of the second injection unit 6 is located closer to the exhaust valve 32 than to the intake valve 31. By shifting the second injection center C2 of the second injection unit 6 toward the exhaust valve 32 in the combustion chamber 4 in this way, more of the main fuel is injected toward the exhaust valve 32, thereby making it easier for the main fuel to burn.

[0048] Furthermore, in the multi-fuel engine 1 of this embodiment, when viewed from the direction of the central axis C of the cylinder 3, a first imaginary line K1 is assumed to divide the combustion chamber 4 into a first region (region) Ar1 where the intake valve 31 is located and a second region (region) Ar2 where the exhaust valve 32 is located, passing through an intermediate position between the intake valve 31 and the exhaust valve 32, and a second imaginary line K2 is assumed to be perpendicular to the first imaginary line K1 at the position of the central axis C, the second injection center C2 of the second injection unit 6 is located on the second imaginary line K2, shifted towards the exhaust valve 32 side from the central axis C. In this way, by shifting the second injection center C2 of the second injection unit 6 towards the exhaust valve 32 side on the second imaginary line K2, more of the main fuel is injected towards the exhaust valve 32 side in the combustion chamber, thereby making it easier for the main fuel to burn.

[0049] Furthermore, the multi-fuel engine and the fuel injection method in the multi-fuel engine of the present invention are not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment. In addition, a part of the configuration of one embodiment can be deleted.

[0050] In the multi-fuel engine 1 of the above embodiment, the first injection unit 5 is positioned in the cylinder head 22 such that the first injection center C1 coincides with the central axis C of the cylinder 3, and the second injection unit 6 is positioned in the cylinder head 22 such that the second injection center C2 is located on the second imaginary line K2, closer to the exhaust valve 32 than the central axis C of the cylinder 3. However, the configuration is not limited to this.

[0051] For example, in a multi-fuel engine 1, when viewed from the direction of the central axis C of the cylinder 3, a first imaginary line K1 is assumed to divide the combustion chamber 4 into a first region Ar1 where the intake valve 31 is located and a second region Ar2 where the exhaust valve 32 is located, passing through an intermediate position between the intake valve 31 and the exhaust valve 32, and a second imaginary line K2 is assumed to be perpendicular to the first imaginary line K1 at the position of the central axis C, as shown in Figure 6, the second injection center C2 of the second injection unit 6 may be located at a position closer to the exhaust valve 32 than the position of the central axis C in the direction of the second imaginary line K2, and also at a position closer to one side (downward in the example shown in Figure 6) than the position of the central axis C in the direction of the first imaginary line K1. In this way, even if the second injection center C2 of the second injection unit 6 is not located on the second imaginary line K2, if it is shifted towards the exhaust valve 32 side from the first imaginary line K1, more of the main fuel will be injected towards the exhaust valve 32 side in the combustion chamber 4, thereby making it easier for the main fuel to burn.

[0052] Furthermore, if the combustion chamber 4 is configured such that more main fuel is injected towards the exhaust valve 32 side (second region Ar2) than towards the intake valve 31 side (first region Ar1), the second injection unit 6 may be positioned such that the second injection center C2 of the main fuel is closer to the intake valve 31 than to the exhaust valve 32 (closer to the intake valve 31 than to the first imaginary line K1). In this way, even if the second injection center C2 of the second injection unit 6 is located towards the intake valve, more main fuel is injected towards the exhaust valve 32 side in the combustion chamber 4, thereby making it easier for the main fuel to burn.

[0053] Furthermore, in the multi-fuel engine 1 of the above embodiment, the diameter of each second injection hole 61 of the second injection unit 6 is the same (i.e., the amount of main fuel injected from each second injection hole 61 is the same), and the multiple second injection holes 61 are arranged at equal intervals in the circumferential direction around the second injection center C2, but the configuration is not limited to this.

[0054] For example, the second injection unit 6 has a second injection hole (injection hole) 61 into which the main fuel is injected. When the combustion chamber 4 is divided into a first region Ar1 where the intake valve 31 is located and a second region Ar2 where the exhaust valve 32 is located, the second injection hole 61 may be configured to inject more main fuel into the second region Ar2 than into the first region Ar1. In this way, by configuring the second injection hole 61 (changing the spacing (pitch) between adjacent second injection holes 61 in the circumferential direction, changing the hole diameter, etc.), more main fuel can be injected into the second region Ar2, thereby making the main fuel easier to burn. In this case, the second injection unit 6 may be positioned in the cylinder head 22 such that the second injection center C2 coincides with the central axis C of the cylinder 3.

[0055] For example, as shown in Figure 7, the second injection holes (injection holes) 61 may be arranged in a plurality at intervals in the circumferential direction around the second injection center C2 of the second injection unit 6, and the diameter of the second injection holes 61 that inject the main fuel into the second region Ar2 may be larger than the diameter of the second injection holes 61 that inject the main fuel into the first region Ar1. By increasing the diameter of the second injection holes 61 that inject the main fuel into the second region Ar2 in this way, more of the main fuel can be injected into the second region Ar2, thereby making the main fuel easier to burn.

[0056] Furthermore, as shown in Figure 8, the second injection holes (injection holes) 61 may be arranged in a plurality at intervals in the circumferential direction around the second injection center C2 of the second injection unit 6, and the number of second injection holes 61 that inject the main fuel into the second region Ar2 may be greater than the number of second injection holes 61 that inject the main fuel into the first region Ar1. In this way, by increasing the number of second injection holes 61 that inject the main fuel into the second region Ar2, more main fuel can be injected into the second region Ar2, thereby making the main fuel easier to burn.

[0057] Furthermore, in the multi-fuel engine 1 of the above embodiment, two intake valves 31 and two exhaust valves 32 are arranged in the cylinder head 22, but the configuration is not limited to this. The cylinder head 22 may also be configured to have one intake valve 31 and one exhaust valve 32, or to have three or more intake valves 31 and three or more exhaust valves 32. [Explanation of Symbols]

[0058] 1…Multi-fuel engine, 2…Engine body, 21…Cylinder block, 22…Cylinder head, 23…Crankcase, 3…Cylinder, 31…Intake valve, 32…Exhaust valve, 4…Combustion chamber, 5…First injection unit, 51…First injection hole, 6…Second injection unit, 61…Second injection hole, 7A…First supply pipe, 7B…Second supply pipe, 10…Piston, 11…Crankshaft, 12…Connecting rod, Ar1…First region, Ar2…Second region, C…Cylinder central axis, C1…First injection center (injection center), C2…Second injection center (injection center), F1…Ignition fuel, F2…Main fuel, K1…First imaginary line, K2…Second imaginary line, P1…First fuel pump, P2…Second fuel pump

Claims

1. A cylinder that defines part of the combustion chamber, A first injection unit that injects ignition fuel into the combustion chamber, The system includes a second injection unit that injects the main fuel into the combustion chamber, The cylinder head of the aforementioned cylinder has an intake valve and an exhaust valve. The cylinder head is equipped with the first injection unit and the second injection unit. The second injection unit injects more of the main fuel into the exhaust valve side of the combustion chamber than into the intake valve side, in a multi-fuel engine.

2. The multi-fuel engine according to claim 1, wherein the injection center of the second injection unit is located closer to the exhaust valve than the intake valve.

3. When considering the cylinder as viewed from the central axis direction, a first imaginary line passing through an intermediate position between the intake valve and the exhaust valve divides the combustion chamber into a first region where the intake valve is located and a second region where the exhaust valve is located, and a second imaginary line perpendicular to the first imaginary line at the position of the central axis, The multi-fuel engine according to claim 2, wherein the injection center of the second injection unit is located on the second imaginary line at a position closer to the exhaust valve side than the central axis.

4. When considering the cylinder as viewed from the central axis direction, a first imaginary line passing through an intermediate position between the intake valve and the exhaust valve divides the combustion chamber into a first region where the intake valve is located and a second region where the exhaust valve is located, and a second imaginary line perpendicular to the first imaginary line at the position of the central axis, The multi-fuel engine according to claim 2, wherein the injection center of the second injection unit is located at a position closer to the exhaust valve side than the position of the central axis in the direction of the second virtual line, and at a position closer to one side than the position of the central axis in the direction of the first virtual line.

5. The second injection unit has an injection hole into which the main fuel is injected, The multi-fuel engine according to claim 1, wherein when the combustion chamber is divided into a first region where the intake valve is located and a second region where the exhaust valve is located, the injection holes are configured to inject more of the main fuel into the second region than into the first region.

6. The injection holes are arranged in a plurality at intervals in the circumferential direction centered on the injection center of the second injection unit. The multi-fuel engine according to claim 5, wherein the diameter of the injection hole for injecting the main fuel into the second region is larger than the diameter of the injection hole for injecting the main fuel into the first region.

7. The injection holes are arranged in a plurality at intervals in the circumferential direction centered on the injection center of the second injection unit. The multi-fuel engine according to claim 5 or 6, wherein the number of injection holes for injecting the main fuel into the second region is greater than the number of injection holes for injecting the main fuel into the first region.

8. The multi-fuel engine according to claim 1, wherein the second injection unit is arranged such that the injection center of the main fuel is closer to the intake valve than to the exhaust valve.

9. In a multi-fuel engine in which intake valves and exhaust valves are arranged in the cylinder head and a cylinder defines a part of the combustion chamber, and ignition fuel and main fuel are injected into the combustion chamber, A fuel injection method for a multi-fuel engine, wherein the main fuel is injected into the combustion chamber in greater quantities from the intake valve side to the exhaust valve side.

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